Black liquor evaporator fouling and cleaning2012-6-29
1. Dirt composition of black liquor evaporator
Black liquor evaporators in the long-term use after scaling, fouling on the heat transfer tube is caused by the main black liquor evaporator coils heat transfer efficiency decreased to the cause. The fouling is prevalent in the black liquor side of the evaporator and in the case of high temperature, high concentrations of the most easy to scale, the analysis found that the dirt in the largest component is calcium carbonate, the main timber of calcium and sodium carbonate in black liquor the reaction of other inorganic dirt sulfate scale, silicate dirt and rust scale. Aluminum silicate scale is generated by the reaction of aluminum in silicate and refractory equipment lining in the black liquor. Chinese paper mills use of grass-based raw materials, high silicon content in the straw, so the black liquor dirt carbonate scale and silicate scale. The organic components in black liquor fouling lignin precipitate, the formation of black liquor organics coking saponification of dirt and organic acids formed in the dirt.
The above thanks to dirt, carbonate scale can be used HCl or HNO3 cleaning with caustic washing and then pickling to remove dirt layer contains a certain amount of silicate scale can be added a certain amount of HF in the pickling to improve the cleaning efficiency. When the scale layer contains a considerable amount of sulfate scale transformation can be used alkaline cleaning, pickling method. Other black liquor fouling, such as lignin evaporator coils scale coking dirt, fiber dirt and some dissolve in water can be washed to remove some soluble alkali available alkaline cleaning to remove, even if the washing, caustic washing can not be removed also in the pickling due to the dissolution of calcium carbonate scale spalling, so the removal of black liquor dirt key descaling.
2. Chemical cleaning
The chemical cleaning method in addition to black liquor fouling process: washing liquid discharge an alkaline cleaning rinse a pickling in a rinse and a passivation.
In alkaline cleaning by immersion and proper warming, heated pass into the steam way to keep cleaning fluid temperature is higher than 80 ℃. Pickling using a closed loop. Cleaning fluid at low prices, to prevent vapor lock, cleaning pump Population Division; filter. In the pickling liquor with nitric evaporator coils acid pickling corrosion and fluid and good corrosion inhibiting effect of acid inhibitor. Descaling rate of 90% or more, the corrosion rate of heat transfer tube is less than 0.1g / (m2 · h), the stainless steel corrosion rate close to zero, in addition to the corrosive effect of film-forming to prevent hydrogen absorption to reduce Fe3 + has The good effect is the most advanced pickling inhibitor. And the process also uses a closed loop. The passivation process and caustic washing as immersion and appropriate warming.
3. High-pressure water jet cleaning
Removal of black liquor dirt physical cleaning methods can be used and removed by hand or mechanical methods of labor and low efficiency, has been basically no longer in use. The high-pressure water jet cleaning method is being increasingly used. The practice shows that the high-pressure water-jet lying cleaning the black liquor evaporation kettle heat transfer tube dirt is an effective method.
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